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Energy Transformation, Cellular Energy & Enzymes (Outline)
• Energy conversions and recycling of matter in the ecosystem. • Forms of energy: potential and kinetic energy • The two laws of thermodynamic and definitions • Chemical reactions and energy transformation • Biochemical metabolic reactions and pathways • Coupling energy consuming biochemical reactions with the energy
releasing reaction of ATP dissociation • Types of cellular work that require energy (ATP) • Role of enzymes in catalyzing biochemical reactions • Biochemical composition of enzymes and the physical and chemical
factors that regulate their activity • Competitive and non-competitive inhibitors of enzymes.
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Figure 1.4-0
ENERGY FLOW
Sun
Inflow of light energy
Producers (plants)
Chemical energy in food
Consumers (animals)
Outflow of heat
Leaves take up CO2 from air; roots absorb H2O and minerals from soil
Decomposers such as worms, fungi,
and bacteria return chemicals to soil
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Figure 1.4-1
ENERGY FLOW
Sun
Inflow of light energy
Producers (plants)
Chemical energy in food
Consumers (animals)
Outflow of heat
Leaves take up CO2 from air; roots absorb H2O and minerals from soil
Decomposers such as worms, fungi,
and bacteria return chemicals to soil
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– Kinetic energy is the energy of motion – Potential energy is stored energy that can be
converted to kinetic energy
• Chemical bonds are a form of potential energy that can be transformed to energize cellular work
Energy is the capacity to do work
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The field of study of energy transformations is Thermodynamics • The First Law of Thermodynamics
Energy can not be created or destroyed, it can be transformed from one form to another
• The Second Law of Thermodynamics Energy transformations increase disorder or entropy of the universe, and some energy is lost as heat.
Energy transformation is not 100% efficient
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Figure 5.2B
Heat
Chemical reactions
ATP ATP
Glucose +
Oxygen water
Carbon dioxide +
Energy for cellular work
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Chemical reactions either store or release energy Endergonic reactions absorb energy and form
products rich in potential energy
Figure 5.3A
Pote
ntia
l ene
rgy
of m
olec
ules
Reactants
Energy required
Products
Amount of energy
required
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Exergonic reactions release energy and yield products that contain less potential energy than their reactants
Figure 5.3B
Reactants
Energy released
Products
Amount of energy
released
Pote
ntia
l ene
rgy
of m
olec
ules
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Cells carry out thousands of chemical reactions some exergonic and others endergonic
Cellular metabolism is the sum of all chemical
reactions that take place inside the cell
Energy coupling uses exergonic reactions to fuel endergonic reactions
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– ATP powers cellular work by shuttling chemical energy
– The energy in an ATP molecule lies in the bonds between its phosphate groups
Phosphate groups
ATP
Energy P P P P P P Hydrolysis Adenine
Ribose
H2O
Adenosine diphosphate Adenosine Triphosphate
+ +
ADP Figure 5.4A
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ATP hydrolysis is the main exergonic reaction used in cellular energy coupling
ATP hydrolysis transfers a phosphate group to a
molecule (phosphorylation). A phosphorylated molecule has a higher potential
energy making it possible for the reaction to take place.
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ATP
ADP + P
Energy for endergonic reactions
Energy from exergonic reactions
ATP is a renewable resource that cells regenerate
Figure 5.4C
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Figure 5.4B
ATP
Chemical work Mechanical work Transport work
P
P
P
P
P
P
P
Molecule formed Protein moved Solute transported
ADP +
Product
Reactants
Motor protein
Membrane protein
Solute
+
Types of Cellular Work
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ENZYMES • Proteins that function as catalysts for
biochemical reactions
• Have a conformation (3D shape) that determines their specific binding to reactants (substrates)
• Lower the energy barriers of chemical
reactions
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For a chemical reaction to begin reactants must absorb some energy, called the energy of activation
Figure 5.5A
EA barrier
Reactants
Products 1 2 E
nzym
e
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A protein catalyst called an enzyme can decrease the energy of activation needed to begin a reaction
Figure 5.5B
Reactants
EA without enzyme
EA with enzyme
Net change in energy
Products
Ene
rgy
Progress of the reaction
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Enzymes, as proteins, have unique three-dimensional shapes that determine which chemical reactions occur in a cell
Each enzyme catalyzes a specific cellular
reaction
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Figure 5.6
Enzyme (sucrase) Glucose
Fructose
Active site Substrate (sucrose)
H2O
1 Enzyme available with empty active site
2 Substrate binds to enzyme with induced fit
4 Products are released
3 Substrate is converted to products
The catalytic cycle of an enzyme
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The cellular environment affects enzyme activity
– Temperature, salt concentration, and pH – Some enzymes require non-protein components Cofactors- metal ions Coenzymes- organic molecules (vitamin
derivatives) – Enzyme inhibitors interfere with an enzyme’s
activity
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– A competitive inhibitor takes the place of a substrate in the active site
– A noncompetitive inhibitor alters an enzyme’s function by changing its shape
Figure 5.8
Substrate
Enzyme
Active site
Normal binding of substrate
Enzyme inhibition
Noncompetitive inhibitor
Competitive inhibitor
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Many poisons, pesticides, and drugs are enzyme inhibitors